In automobile roof structures, a pair of left and right roof side rails is provided extending in a front-rear direction on both side edges, left and right, of a roof panel. A roof reinforcement member is provided across the roof side rails, in a vehicle width direction, along the underside of the roof panel. From the viewpoint of, for instance, workability during the roofing operation, the roof reinforcement member is ordinarily shorter than the distance between the left and right roof side rails. The roof reinforcement member is connected to the roof side rails via brackets at the ends of the roof reinforcement member.
During a vehicle side collision, a center pillar of the vehicle is acted upon by a load that bends and deforms the center pillar into a V shape that points toward the interior of the vehicle. As a result, a rotational moment is generated that twistingly deforms the roof side rail, and that pushes the lower edge of the roof side rail toward the vehicle interior, at the joint of the roof side rail with the upper end of the center pillar and at nearby positions.
When the roof reinforcement member is solidly connected to the roof side rails via the brackets, the connection positions stand at the upper ends of the roof side rails. Therefore, a substantial bending force acting on the roof reinforcement member may cause the latter to bend. The roof panel as a whole may become extensively damaged as a result.
Several measures have been conventionally devised with a view to preventing the rotational moment of the roof side rails from being transmitted to the roof reinforcement member during a side collision (for instance. JP-A-10-100936).
FIGS. 4 and 5 illustrate an example of such a conventional structure. A bracket 6 made up of a metal plate is provided on a roof side rail 2, at the joint thereof with a center pillar 3. The bracket 6 has tongue-like protruding pieces 61, 61 that protrude toward the vehicle interior. The protruding pieces 61, 61 are inserted into the end of a roof reinforcement member 4, which has a corrugated cross section and is provided on the underside of a roof panel 1, to cause the bracket 6 to engage thereby with the roof reinforcement member 4. An outer end 62 of the bracket 6 on the exterior of the vehicle is fixedly bolted to an interior a side surface 21 of the roof side rail 2.
As shown in FIG. 6, when the roof side rail 2 is twistingly deformed during a side collision, the protruding pieces 61, 61 of the bracket 6 deform upward as a result, and shift relative to the roof reinforcement member 4, so that virtually no bending force acts on the roof reinforcement member 4.